Somatotropin (ST), sometimes referred to as Growth Hormone (GH) in the art, is normally produced by the pituitary throughout an animal's life, although apparently in higher amounts during the pre-adult period. ST is known to promote skeletal growth, nitrogen retention, protein synthesis and to affect glucose and lipid metabolism. Accordingly, ST is recognized as a general anabolic agent.
Although the mechanism of ST activity is not well understood, it has been demonstrated that the administration of exogenous ST of the same species as the test subject markedly increases the rate of growth, weight gain, and meat production in animals and, for porcine somatotropin, improves the chemical composition of the edible meat. See, E. J. Truman, "Some Effects of Pituitary Anterior Growth Hormone On Swine", Thesis; Purdue University (April 1953),
ST can be isolated from excised pituitary tissue. See, e.g., C. H. Li, J. Biol. Chem. 211, 55 (1954). ST can also be obtained from genetically engineered microorganisms containing recombinant DNA which specifies the production of ST. See, e.g., P. H. Seeburg, et al., Nature, 276, 795-798 (1978); P. H. Seeburg et al., Nature, 270, 486-494 (1978); J. A. Martial, Science. 205, 602-607 (1979).
Porcine Somatotropin (pST), also referred to in the art as Porcine Growth Hormone (pGH), is a polypeptide synthesized in and secreted from the anterior lobe of the pituitary. The preparation of pST is well known in the art. For example, U.S. Pat. No. 3,201,382 discloses a process for isolating animal somatotropins such as pST from excised pituitary tissue. European Patent Application No. 83305717.7, filed Sep. 26, 1983, with Publication Number 104,920 discloses DNA sequences, recombinant DNA molecules and transformed host suitable for producing pST and European Patent Application No. 83306730.9 filed Apr. 11, 1983, with Publication Number 111,389 discloses DNA sequences and transformed hosts for producing pST.
Lysine is an essential amino acid required for normal animal growth and development. Lysine is present in varying amounts in an animal's diet. However, particularly in animal husbandry, supplementary lysine must be added to an animal's diet to insure proper nutrition.
In addition, high dietary lysine has been used in the art to promote growth, improve weight gain and increase feed utilization efficiency. U.S. Pat. No. 3,868,467 issued to Olson discloses a feed composition comprising high lysine corn to enhance rapid growth of young pigs. The composition also can comprise a further addition of lysine as a separate additive, wherein the lysine comprises up to 0.25% of the total weight of the composition. U.S. Pat. No. 4,172,148 issued to Hauck et al discloses the addition of the trichloroethyl ester of lysine to enhance the growth and feed efficiency of ruminants. However, greater gain and improved feed utilization has been observed with diets containing higher concentrations of lysine: See, Baker et al., Lysine Requirement of Growing Pigs at Two Levels of Dietary Protein, 40 J. Anim. Sci. 851 (1975); Brown et al., Lysine Requirement of the Finishing Pig for Maximum Rate of Gain and Efficiency, 37 J. Anim. Sci. 708 (1973); Kornegay et al., Supplementation of Lysine, Ammonium Polyphosphate and Urea in Diets for Growing-Finishing Pigs, 34 J. Anim. Sci. 55 (1972); Williams et al., The Lysine Requirement of the Growing Boar Versus Barrow, 58 J. Anim. Sci. 657 (1984).
Individually, both somatotropin and high dietary lysine are known to promote growth in swine. However, methods for using known growth promotants in combination to synergistically promote growth are needed; synergistic combinations lower the dosages required for the individual agents and therefore reduce the cost of the materials needed to promote growth.